Fatty acids and triglycerides are used widely in the food industry, in animal nutrition, in cosmetics and in the pharmaceutical sector. Especially valuable and sought-after unsaturated fatty acids are what are known as conjugated unsaturated fatty acids. Conjugated polyunsaturated fatty acids are relatively rare in comparison with other polyunsaturated fatty acids. Examples of conjugated fatty acids are the conjugated linoleic acids (CLA; conjugated linoleic acid), α-parinaric acid (18:4 octadecatetraenoic acid), eleostearic acid (18:3 octadecatrienoic acid), the conjugated linolenic acids, dimorphecolic acid and calendulic acid (see scheme 1).

CLA is a collective term for positional and structural isomers of linoleic acid which are distinguished by a conjugated double bond system starting at carbon atom 8, 9, 10 or 11. Some examples are shown in scheme 2.
Geometric isomers exist for each of these positional isomers, that is to say cis-cis, trans-cis, cis-trans, trans-trans.

The CLA isomers (9Z,11E)-CLA and (10E,12Z)-CLA are known as the biologically active isomers. CLA is found predominantly in foodstuffs of animal origin. High CLA concentrations are found in particular in the meat and in dairy products of ruminants: approx. 3 to 4 mg of CLA/g fat in beef and lamb (Chin et al. (1992) J Food Comp Anal 5:185-197) and approx. 3 to 7 mg of CLA/g fat in dairy products (Dhiman et al. (1999) J Dairy Sci 82:2146-56), where (9Z,11E)-CLA at a concentration of approximately 80% is in each case the predominant isomer. Higher plants only contain traces of CLA, with the two biologically active CLA isomers not having been found in plants to date.
A range of positive effects have been found for CLA; thus, the administration of CLA reduces the body fat in humans and animals and increases the rate at which feed is converted into body weight in animals (Park et al. (1997) Lipids 32:853-858; Park et al. (1999) Lipids 34:235-241; WO 94/16690; WO 96/06605; WO 97/46230; WO 97/46118). The administration of CLA also has a positive effect on, for example, allergies (WO 97/32008) or cancer (Banni et al. (1999) Carcinogenesis 20: 1019-1024, Thompson et al. (1997) Cancer Res 57:5067-5072). An antiarteriosclerotic effect of CLA has also been confirmed (Wilson et al. (2000) Nutr Res 20:1795-1805). Studies were carried out with isomers and with isomer mixtures.
CLA can be synthesized by alkaline isomerization of linoleic acid. Vegetable oils with a high linoleic acid content are predominantly used on an industrial scale, for example sunflower oil, safflower oil. Heating to above 180° C. under alkaline conditions catalyzes two reactions:    (1) the fatty acid ester bonds of the triglyceride skeleton are hydrolyzed and the free fatty acids are liberated,    (2) unconjugated unsaturated fatty acids with two or more double bonds are conjugated.
Commercially available CLA oils contain a mixture of various CLA isomers and other saturated and unsaturated fatty acids. Owing to the presence of these biologically inactive and unnatural isomers, laborious purification of the biologically active isomers (9Z,11E) CLA and (10E,12Z) CLA is required, or it must be demonstrated that the isomer mixture does not represent a health hazard for humans and animals. It has hitherto not been possible to produce individual CLA isomers by alkaline isomerization in an economically relevant process. Fractional crystallization makes it possible to concentrate the isomers (9Z,11E)-CLA and (10E,12Z)-CLA, respectively. However, it is not possible in all of the abovementioned processes to prepare individual isomers in high quality. In the abovementioned processes, the reaction products are usually converted into methyl or ethyl esters so that the natural form of CLA, viz. the free fatty acids or the triacyl glyceride, are not available.
These disadvantages of chemical conversion can be overcome by carrying out the conversion of linoleic acid into CLA by biocatalysis. Various microorganisms of the rumen of ruminants are capable for example of converting linoleic acid into CLA during the biohydrogenation process. This is effected by the enzymatic activity of a CLA isomerase, inter alia. This enzymatic activity was described in Butyrivibrio fibrisolvens (Kepler and Tovee (1966) J Biol Chem 241:1350), Propionibacterium acnes (Deng et al., 1st International Conference on CLA, 2001, Alesund, Norway), Clostridium sporogenes and Lactobacillus reuteri (WO 99/32604; WO 01/00846). The CLA isomerases described to date utilize free fatty acids as substrate. The genes encoding CLA isomerase from Lactobacillus reuteri and Propionibacterium acnes were cloned, and the isomerase from Propionibacterium was expressed functionally in heterologous microorganisms. While the bioconversion of linoleic acid into CLA by microorganisms has qualitative advantages over alkaline isomerization, it is economically disadvantageous, owing to the fermentation costs, and only yields free fatty acids, but no triglycerides. However, free fatty acids have disadvantageous olfactory properties and are essentially unsuitable for use in the food- and feed sector. A subsequent conversion of the free fatty acids—for example glycerol or gylcerides with lipase catalysis—is possible, but complicated.
The methods which are based on bacterial CLA isomerases can always be applied to other organisms. So far, it has been shown that CLA isomerases convert free linoleic acid into CLA (Cepler and Tove (1967) J Biochem Chem 242:5686-5692). In higher organisms such as, for example, plants, linoleic acid predominantly exists in esterified form. Lipids such as triacyl glycerides constitute the storage form, while thioesters such as acyl-CoA constitute the active form of the fatty acid.
Fatty acids with trans double bonds are extremely rare. The seed oil of some plants contains fatty acids with double bonds in the trans position. Thus, an E5-fatty acid has been detected in the seed oil of various Thalictrum species (Rankoff et al. (1971) J Amer Oil Chem Soc 48:700-701). Moreover, E5-desaturase activity has been described in Aquilegia vulgaris (Longman et al. (2000) Biochem Soc Trans 28:641-643). However, no plants have been described which contain either trans-vaccenic acid (E11-octadecenoic acid) or E10-octadecenoic acid.
It is known that the desaturation of fatty acids in plants can take place mainly by two mechanisms:    (1) in plastids, fatty acid ACP esters are desaturated by a soluble desaturase, predominantly at position 9, and    (2) on the endoplasmic reticulum, membrane lipids, especially phosphatidyl cholins, are preferentially further desaturated at positions 6, 12 and 15 by membrane-bound desaturases.
In some plants, conjugated fatty acids are produced by the activity of a conjugase (Crombie et al. (1984) J Chem Soc Chem Commun 15:953-955; Crombie et al. (1985) J Chem Soc Perkin Trans 1:2425-2434; Fritsche et al. (1999) FEBS Letters 462: 249-253; Cahoon et al. (2001) J Biol Chem 276:2637-2643; Qiu et al. (2001) Plant Physiol 125:847-855). The biosynthesis of conjugated fatty acids such as calendulic acid, eleostearic acid or punicic acid proceeds via the desaturation of oleic acid to linoleic acid by a D12-desaturase and a further desaturation in conjunction with a rearrangement of the Z9- or Z12-double bond to the conjutrienic fatty acid by a specific conjutriene-forming desaturase (conjugase). Besides the production of calendulic acid, Qui et al. (2001) Plant Physiol 125:847-855) also describe the production of conjugated linoleic acid by the enzymatic activity of conjugase. However, the disadvantage of this secondary activity is that the enzymatic activity gives rise to the undesired 8,10-isomer of the conjugated linoleic acid.
Pheromone desaturases from lepidopterans display a wide range of substrate specificities and desaturation mechanisms (Roelofs and Wolf (1988) J Chem Ecol 14:2019-2031; Roelofs (1995) Proc Nat Acad Sci USA 92:44-49; Tillman et al. (1999) Insect Biochem 29:481-514). These enzyme activities cause the production of unusual unsaturated fatty acid CoA derivatives with a wide range of chain lengths and with double bonds at different positions and with different configurations. They act as starting material for the biosynthesis of pheromones. Liu et al. describe an E11-desaturase from the pheromone gland of a moth species (“light brown apple moth”), which is likely to play a role in pheromone biosynthesis (Liu W T et al. (2002) Proc Natl Acad Sci USA 99(2):620-624.
Knipple et al. (Genetics 2002 December; 162(4):1737-52) compare various integral membrane desaturases from moths and flies which have been isolated from the pheromone glands of these insects. A fragment of an acyl-CoA desaturase (PgosVASQ) from Pectinophora gossypiella is described. The corresponding sequence has been deposited under the GeneBank Acc. No.: AF482921. Neither the complete sequence nor the specific activity of the desaturase are described. It was named merely on the basis of homologies with other desaturases.